Polymorphism

The existence of more than two distinctive forms (usually in terms
of
plumage)
within a
species.
Each form, which is not regarded
as a
subspecies,
is called a 'morph'. The males of the Ruff Philomachus
pugnax are polymorphic, having a great variety of colour and
pattern. Species with just two morphs are said to show
dimorphism.